3DMark 11 likely gives somewhat of skewed impression, and that's because this benchmark is intended to scale with both GPU and CPU performance, not just GPU performance.
Both high-end cards are able to achieve a Performance score of around 10,000 points, but as you can see you need an Intel Core i7 for that to happen. With an Intel Core i5 3570K or AMD FX-6300 you get close to that. With less powerful AMD and Intel processors the scores end up around 7,000 points.
With Extreme settings we see a similar picture. You need a Core i7 to get the top score, but even with an Intel Pentium there's only a 10-percent performance drop. Here the CPU forms a pretty limited bottleneck.